This invention relates generally to fuel burner control system and, more particularly, to a burner control system that utilizes a resistive heater element for igniting fuel emanating from a fuel burner.
The continuing interest in reduced energy consumption and increased safety has resulted in the development of safer and more fuel efficient burner control systems. Of particular note has been the extensive replacement of pilot burner systems with systems employing electronic ignitors that are energized only when main burner ignition is desired. Such electronic ignitor systems eliminate the fuel loss entailed by pilot burners during periods in which full burner operation is not required. Spark ignitors and resistive heater elements are two common mechanisms utilized to ignite fuel in electronic burner control systems. Although spark ignitors exhibit a number of desirable characteristics, resistive heating elements have certain inherent features that offer unique operational advantages. For example, a resistive heater element can establish a larger thermal mass than a conventional spark ignitor and, therefore, can provide more reliable ignition of less than optimum fuel and air mixtures. In addition, the positioning of a resistive heater ignitor with respect to a burner is less critical than that required for an analogous spark ignitor.
Disclosed in U.S. Pat. No. 4,298,335 is a burner control system in which a resistive heater element functions both as a fuel igniting mechanism and as a detection electrode for deriving flame rectified current. The dual functions simplify and reduce the cost of the control system. However, the heater element in the disclosed system can function only alternatively as an ignitor mechanism or a flame detection electrode. Consequently, the system can not provide simultaneous ignition and flame detection periods. That factor reduces the operational flexibility of the system and can result in nuisance lock-outs.
The object of this invention, therefore, is to provide an improved burner control system with a resistive element that functions both as an ignition mechanism and as a flame detection electrode.